At PAX East, the answer regarding implementing flight in A Realm Reborn areas was that doing it in the short term would likely delay the 4.0 release since we'd have to model terrain that we can't see from the ground but would be able to see were we able to freely fly.

Why not just put flight boundaries such that we still can't get to the "wrong" side of such scenery? We already hit invisible walls when we try to fly too far in Heavensward areas. Just put those boundaries a bit closer as needed in ARR areas.